At age 14, began playing the violin professionally in New York City. Under the stage name Hal Hope, he led nightclub and society bands. By 1936, he had taken up the theremin and begun featuring it in publicity for his engagements.

In 1941, Hoffman moved to Los Angeles, where he established a medical practice and had little time for musical activity. But as the only theremin player in Local 47 of the Musicians Union, he got the call in 1945 when composer Miklos Rosza decided he wanted to use a theremin in the score to Spellbound. Hoffman began performing under his real name; he was customarily referred to as "Doctor" because he was also a podiatrist.[1] In the wake of the film's success, he was asked to play on many more soundtracks; for instance, The Day the Earth Stood Still (1951). He was in demand for horror movie and sci fi soundtracks through the end of the 1950s.